Hot-Dip by Thomas Consultant,
Galvanizing
Technology
H. Cook Hot Springs,
S.D.
T
his article quantifies results of new technologies in a specific hot-dip galvanizing plant. Future articles will quantify results of these technologies in additional plants in which these technologies have been adopted in different ways and in different sequences. Steel products of different geometries and types respond differently to these technologies. This article suggests universal measurement methods so as to compare various galvanizing plants. Above all, the main purposes of this article are to enable galvanizers to lower operating costs, attain a higher quality product, and to be more profitable. Hot-dip galvanizing is undergoing a revolution; it provides very long corrosion protection and is very competitive with other steel coatings. Readers are invited to fill out a Data Sheet (Fig. 1) and return it to the author’ so that more hot-dip galvanizing articles can appear in Metal Finishing. One Data Sheet is required for each kettle and any units are fine provided that they are labeled. Galvanizers’ names, suppliers, and products will be kept confidential.
Using data from Figure 2, the zinc on the steel should be: (Lb Zinc on Steel) = (27,409,100
lb) X (2) X (0.0055
in.)/(0.1875
in.)
The 0.0055 in. is the average (4+7)/2 reported as (mils) average zinc on steel (5.5/1,000) converted to inches (0.0055). The 0.1875-in. thick steel is 3/ls in. converted to a decimal. Doing the math of the above algebraic equation gives: (Lb Zinc on Steel) = 1,608,OOO lb (not possible) Clearly there cannot be 1,608,OOOlb of zinc on the steel because only 1,395,500 lb of zinc total have been consumed. Either the zinc thickness must be thinner (than 5.5 mils) or the steel thickness must be thicker (than 0.1875 in.) or both. After discussions with the galvanizer, more accurate values are 4.58 mils zinc on steel and 0.22-in. thick steel. The zinc on the steel more accurately is: (Lb Zinc on Steel) = (27,409,100 lb) X (2) X (0.00458MO.22 in.) (Lb Zinc on Steel) = 1,141,200 lb
ZINC
BALANCE
Figure 2 is a completed Data Sheet for an excellent “Dry Kettle” (no molten topflux on the molten zinc), job shop galvanizer. The zinc balance is calculated to determine where the zinc is consumed. In this case on the steel, in dross, in ash, and “stripped” (dissolved) in acid. (Lb Zinc on Steel) = (lb steel) x (2) x (zinc thickness) X (1.W
(steel thickness) X (1.1) The above formula is used to calculate the zinc on the steel. The “2” in the numerator accounts for coating both sides of the steel. The “1.1” in the numerator provides 10% more zinc for drips and “runs.” The “1.1” in the denominator accounts for the differences in the densities of zinc and steel. Because there is a “1.1” in both numerator and denominator the algebra simplifies to: (Lb Zinc on Steel) = (lb steel) x (2) x (zinc thickness)/(steel thickness)
To calculate the zinc in the dross the following formula and data from Fig. 2 are used: (Lb Zinc in Dross) = (lb dross) X (0.97) (Lb Zinc in Dross) = (175,180 lb) X (0.97) (Lb Zinc in Dross) = 169,900lb To calculate the zinc in the ash the following formula is used: (Lb Zinc in Ash) = (lb ash) X (0.90) (Lb Zinc in Ash) = (89,845 lb)
August2000
57747
(0.90)
(Lb Zinc in Ash) = 80,900 lb To calculate the zinc “stripped” (dissolved) in “spent” acid the formula is: (The 0.75% zinc in spent acid comes from Fig. 2, in the “Acid 2” tank section. The 0.01 converts % to fractional zinc in spent acid.) (Lb Zinc Stripped) = (gal. spent acid) x (%Zn in spent) x (spent density)
X (0.01)
(Lb Zinc Stripped) = (30,000
'HC 52 Box 120-B, HotSprings,SD
X
gal) X (0.75) X (0.01) X (11 lb/gal)
(Lb Zinc Stripped) = 2,500 lb 19
Fax Address Phone One Year Data From E-Mail -To Temp. Concentrations/Conditions Width Depth % Other % FiretubeCoil- Suds- Oil SorbentNaOH ~ ~ FlowingStagnantCountercurrentOil Sorbent____ ~ PH % Zn % Inhib. % SudsWorking: Acid % Fe % Fe % Zn % Oil SorbentAt Spent: Acid At Spent: Acid % Fe % Zn % Oil Sorbent__ ___ CountercurrentTank LinedFlowingStagnantPHFlowingCountercurrentTank LinedStagnantPHBe’ Fe % so4 % pHACNSudsWettingAgent~ Al % Pb % Ni % Bi % Other % ~ % Other % White Rust -O/O -Inches Sludge -pH-.-- Cr (Lbs) Steelmzed Natural Gas Cost ($/Therm) (In) Average Steel Thickness Natural Gas Cost ($/Year) Electricity Cost ($/KWH) (Mils) Average Zinc on Steel (Mils) Desired Zinc on Steel Electricity Cost ($/Year) (Lbs) Zinc Used Zinc Cost ($/Lb) Dross Value ($/Lb) (Lbs) Dross Dry Ash Value ($/Lb) (Lbs) Dry Ash (Lbs) Wet Skims Wet SkimsValue($/Lb) (Lbs) Flux Used(For Solution) Flux Cost ($/Lb) (Lbs) Topflux Used Gross Production Labor Including All Benefits ($/Hour) (Gallons) “Spent” Acid “Spent” Acid Cost ($/Gal) Steel: Job Shop% Captive -...-.% Structural-% Spin% Bolts -% Cast% Silicon Killed-% Rack Jigs: Have About-% the Surface Area of the Steel. Steel Re-Racked After FluxingJigs Stripped Every Caustic: Steel Product Put Into Caustic -% Temp of Exhaust Gases From Fire TubesInches Sludge DepthAcid: H2S04HCIHeating Method/Coil Metal Acid Recoveryor DisposalOil SorbentFlux: Heating Method/Coil Metal Tank Lined- Inches Sludge DepthDump- Purify- Frequency pH Measured By: pH Meter- “Blue Indicator”pH PaperpH Adjusted By: NH40H- HCI- Zinc- Drossor in -Inches Process Tanks (Caustic/Acid/Flux): Sit on Cross BeamsFlat on Concreteof Containment Pit Liquid Containment Pit Divided Into Three SectionsSteel Product Drain-Time Over Process Tanks Seconds Time (Minutes) Steel in Tanks: Caustic Rinse Acid Rinse Flux Zinc Kettle Kettle: Number BurnersFlat Flame;_ End Fired- Burner Capacity (BtulHour) Kettle Capacity (LblHr) Wall Cleaning: Frequency PickaxeDrawknifeAirhammer“Canopener”Kettle EnclosureThere are -Inches of Directly Under the Kettle. Temp of the Furnace Pit Kettle Life-Years Flue Heat Used to Heat Process TanksTemperature Outer Furnace Wall Kettle Covered-Hours/Week Temperature of Exhaust Gases at Kettle Furnace Exit: Kettle Covered Idle Full Production Maximum Inches from Top Edge of Kettle to Zinc SurfaceWater Table Feet From Ground Level Zinc Clean-Up: Number Paint Cans Used/Ton Steel _ Sanding Disks Used/Ton SteelFiles Used/Ton SteelGalvanizing Rejects: Total-% Refluxed Only -% Acid Stripped -% Causes of Rejects Drossing: Kettle TempDays Between DressingHours to DrossInches Lead in KettleClam- ScoopMaximum Inches Dross: Before Drossing Six Hours After Drossing Number Guys to Dross Skimming: Sinking SkimmersFloating Steel SkimmersWood SkimmersManual Ash BoxAuto Ash BOXReverse Archimedes ScrewMinimum Ash Box Stand-Off from Walls Inches Lbs Ash/Barrel Cranes: Kettle Withdrawal Speed FtiMin ElectricAir- NumberBreakdown Time-% Capacity Lbs Spin Baskets: Hours Used Between CleaningLifetime (Months)Special AlloyDimensions -High -Dia. Turn-Around Time Working Days. Total Production (Labor Only) Guys Working -Hours/Week Each Guy. Total Customers’ Complaints/Month Nature of Complaints Quad Lower IQM Slower Univ. Lead Nickel Bismuth Spin Flux Kettle T Withdraw Racking Alloy Alloy Alloy Express
Company Person Length Caustic Rinse Acid 1 Acid 2 Strip __ Rinse 1 Rinse 2 Flux Kettle Quench -
YEAR 1 83 T 84 1 85 1 86 / 87 1 88 1 89 1 90 1 91 1 92 I 93 I 94 I 9s %GZU 1 1 Dr. Thomas H. Cook (c) 2000 Phone/Fax 605 745 4567 Figure
20
1. Data
1 96 I 97 I 98 I gg I 88 E-Mail
[email protected]
sheet.
Metal
Finishing
Company Address Phone Fax Person E-Mail One Year Data From-Jan 1,1999_To- Dee 31,1999Temp. Concentrations/Conditions Length Width Depth Caustic-458 9-170 F- NaOH % Other % Firetube-X- Coil- Suds-X- Oil SorbentRinse -32 - -- 7 FlowingStagnant-XCountercurrentOil Sorbent-- 9 -AmbPH-1 3Acid 1 -45-7 9 -AmbWorking: Acid-G-IO-% Fe-- 5 % Zn % Inhib.-Yes- % SudsAcid 2 -33.5 7 9 -AmbAt Spent: Acid-P- 3-% Fe-12-% Zn-0.75-% Oil SorbentAt Spent: Acid % Fe strip %Zn % Oil SorbentRinse 1 _33.5 7-FlowingStagnant-XCountercurrentTank Lined--X -- 9 -AmbPH-ORinse 2 --FlowingStagnantCountercurrentTank LinedPH-.Flux -160 F- Be’-12- Fe-0.2-% SO4-% pH5- ACNSuds-X- Wetting Agent-X-33.5 -7-gKettle -33.5 -7-825 F- Al-0.0025-% Pb-0.006-% Ni-0.027% Bi-0.0799% Other % -g% White Rust-% -Inches Sludge Quench % Other PHCr -27,409,100 (Lbs) Steel Galvanized Natural Gas Cost ($iTherm) $ o-550.1875-(In) Average Steel Thickness Natural Gas Cost ($/Year)-$174,0004 To 7- (Mils) Average Zinc on Steel Electricity Cost ($/KWH) $0.083 To 5-(Mils) Desired Zinc on Steel Electricity Cost ($/Year)$35,000-1,395,500 (Lbs) Zinc Used Zinc Cost ($/Lb) $0.565(Lbs) Dross Dross Value ($/Lb) -175,180 !§0.33-89,845 (Lbs) Dry Ash Dry Ash Value ($/Lb) $0.195(Lbs) Wet Skims Wet SkimsValue($/Lb) (Lbs) Flux Used (For Solution) Flux Cost ($/Lb) $0.60 (Lbs) Topflux Used Gross Production Labor Including All Benefits ($/Hour) “Spent” Acid Cost ($/Gal) -~ $ 2.00-30,000 (Gallons) “Spent” Acid Steel: Job Shop-IOO-% Captive-O-% Structural % Spin-O-% Bolts-O-% Cast-O-% Silicon Killed% Rack Jigs: Have About% the Surface Area of the Steel. Steel Re-Racked After FluxingJigs Stripped Every Inches Sludge DepthCaustic: Steel Product Put Into Caustic-IOO-% Temperature of Exhaust Gases From Fire TubesAcid: H2S04HCI-X- Heating Method/Coil Metal Acid Recoveryor Disposal-X- Oil Sorbent.-.Flux: Heating Method/Coil Metal-Carbon Sticks- Tank Lined-X- Inches Sludge Depth-3- Dump- Purify-X- Frequency-4 MonthspH Measured By: pH Meter- “Blue Indicator”- pH Paper-XpH Adjusted By: NH40H-XHCI- Zinc- DrossInches of Containment Pit Liquid Process Tanks (Caustic/Acid/Flux): Sit On Cross Beams-XFlat on Concreteor in Seconds Containment Pit Divided Into Three Sections-NoSteel Product Drain-Time Over Process Tanks Rinse Acid Rinse Flux Zinc Kettle Time (Minutes) Steel in Tanks: Caustic Kettle: Number Burners-IS- Flat Flame-X- End FiredBurner Capacity (Btu/Hour) -7OO,OOO- Kettle Capacity (Lb/Hr)-lO,OOOWall Cleaning: Frequency-WeeklyPickaxe-X- DrawknifeAid-rammer-X- “Canopener”-. Kettle EnclosureThere are -0.2-Inches of -InsulationDirectly Under the Kettle. Temp of the Furnace Pit Kettle Life-7 - 8-Years Flue Heat Used to Heat Water Process TanksKettle Covered-80 Hours/Week Temperature Outer Furnace Wall Full Production Temperature of Exhaust Gases at Kettle Furnace Exit: Kettle Covered Idle Water Table Feet From Ground Level Maximum Inches From Top Edge of Kettle to Zinc Surface Sanding Disks Used/Ton Steel Files Used/Ton Steel Zinc Clean-Up: Number Paint Cans Used/Ton Steel Galvanizing Rejects: Total-O.l-% Refluxed Only-90-% Acid Stripped-IO-% Causes of Rejects Drossing: Kettle Temp-820Days Between DrossinglHours to Dross-lInches Lead in Kettle-O- ClamScoop-XNumber Guys to Dross Maximum Inches Dross: Before Dressing-3Six Hours After Dressing-0.754 Skimming: Sinking SkimmersFloating Steel SkimmersWood Skimmers-XManual Ash Box-XAuto Ash BoxMinimumAsh Box Stand-Off from Walls -- 3 Inches Lbs Ash/Barrel Reverse Archimedes ScrewCranes: Kettle Withdrawal Speed Ft/Min-5- Electric-XAir- Number-8- Breakdown Time-l-% Capacity (Lbs) High Spin Baskets: Hours Used Between CleaningDia. Lifetime(Months)Special AlloyDimensions Turn-Around Time-S-Working Days. Total Production (Labor Only) Guys-22-Working-SO-Hours/Week Each Guy Total Customers’ Complaints/Month-5Nature of Complaints- Lost Steel Parts, Poor Zinc Drainage, Dull Galv (Si Steel)Bismuth Spin Quad Lower Slower Univ. Lead Nickel Technology Dry IQM Alloy Alloy Express Kettle Flux Kettle T Withdraw Racking Alloy Started Aug 97 Ott 98 Date July84 June86 88? act 93 YR 1 84 1 85 1 86 1 87 1 88 1 89 1 90 1 91 1 92 1 93 1 94 / 95 1 96 1 97 1 98 / 99 1 00 GZ 1 10.29 1 11.61 1 8.38 1 6.42 1 6.75 1 6.43 1 6.34 1 6.55 1 6.55 1 6.41 1 6.35 1 6.18 1 6.12 1 6.06 j 5.7 1 5.08 1 5.2 Phone/Fax 605 745 4567 E-Mail
[email protected] Dr. Thomas H. Cook (c) 2000 Figure
August
2. Completed
2000
data
sheet. 21
The zinc balance is shown in Table I. The calculated total zinc used of 1,394,500 lb is only 1,000 lb less than the 1,395,500 lb reported in Figure 2. In the early days of galvanizing work the author considered good practice as 80% or more zinc on the steel, less than 10% zinc in dross, less than 7% zinc in ash (using a manual ash box), and zinc stripped in acid as quite variable depending on operations (e.g. racking, reracking, rack size, hooks, wires, etc.) Although zinc balance is required, unfortunately it can be misleading. For example, very thick zinc coatings would make zinc in dross, ash, and stripped appear quite small. In the next section much better means of measurement and evaluation are presented. PROCESS
NORMS
Unlike zinc balance, process norms are either based on steel galvanized or on absolute methods of measurement. In this way the galvanizer can be evaluated on an absolute scale. To calculate %Gross Zinc Usage (%GZU) the following formula and data from Figure 2 are used: %GZU = (lb zinc used) X (lOO%)/(lb %GZU
steel)
= (1,395,500 lb) x (100%)/(27,409,100lb)
%GZU = 5.09% The author introduces the concept of %Standardized Gross Zinc Usage (%SGZU), which fixes the steel thickness at l/4 in. In this way all galvanizers’ steel would have the same surface area relative to weight. %SGZU is defined as: %SGZU = (%GZU)
X
(average steel thickness)/(0.25
%SGZU
= (5.09%)
x
(0.22 in.)/(0.25
%SGZU
= 4.48%’
in.)
%Dross/Steel = (lb dross) X (lOO%)/(lb steel) x
(100%)/(27,409,100lb)
%Dross/Steel = 0.64% %Ash/Steel
= (lb ash) X (lOO%)/(lb
steel)
%Ash/Steel = (89,845 lb) x (100%)/(27,409,100 lb) %Ash/Steel
= 0.33%
%Plant Utilization %Plant
Utilization
is defined as:
=
(million lb of steel) X (lOO%)l(kettle length in ft) %Plant Utilization = (27.4 million lb) x (1000/0)/(33.5ft) %Plant
Utilization
= 81.8%
The %plant utilization formula above generally applies to a kettle 5 feet wide. If, for example, a 22
I. Zinc
Balance
Lb zinc on the steel Lb zinc in dross Lb zinc in ash
Lb zinc stripped in acid Lb zinc total
1,141,200 169,900 80,900 2,500 1,394,500
81.8% 12.2% 5.8% 0.2% 100.0%
lb lb lb lb lb
kettle were 10 feet wide (a most unusual case) then twice as much production would be required to attain the same %plant utilization. Lb/Man-Hour
= (lb of steel)/(guys)
Lb/Man-Hour
= (27,409,100 lb)/(22) X (50 wk/yr)
Lb/Man-Hour
= 498 lb
x
(hr/wk) x
x
(wk/yr)
(50 hr/wk)
Calculations for kettle capacity (actually maximum continuous kettle capacity) will be shown in a future article. The basis for these calculations is: 10,000 Btu/ft’/hr heat throughput through the available side-wall heating zones (for this galvanizer only 8,470 BtuJft21hr was used); six-in. upper and g-in. lower insulated (no heat throughput) zones; 6,700 Btu/ft2/hr convected and radiated heat losses at the zinc air interface (reduced by 25% for a kettle having an enclosure; the case with this galvanizer); 50% efficiency for a flat-flame furnace; minimum 6-in. castable high-strength insulation under the kettle (not the case with this galvanizer); and a well insulated outer furnace wall (not the case with this galvanizer). The calculations give a maximum continuous capacity of Kettle
in.)
%Dross/Steel is defined as; %Dross/Steel = (175,180 lb)
Table
Capacity
= 25,600 lb steel/hr(calculated)
This galvanizer is able to galvanize only about 10,000 lb steel/hr, not because of the kettle capacity but because insulation around the furnace is insufficient and the floor plates get so hot that they expand and buckle-up. Kettle Firing is defined by: Kettle Firing = (Btu/ft’Lkr side-wall heating zone heat throughput) x (100%)/(10,000 Btulft’kr side-wall heating zone heat throughput) Kettle Firing = (8,470 Btu/ft’/hr) Kettle
Firing
X
(100%)/(10,000
Btu/ft”/hr)
= 84.7%
If this kettle had been fired at 100% then the maximum continuous capacity would have been 32,000 lb steel/hi-. The “up-side” to under firing a kettle is that the kettle life would have been extended from about 6 years to predictably about 12 years. The next item also is a predictor of kettle life. Metal
Finishing
Table
II. Process
Norms
5.09% 4.48% 0.64% 0.33% (Manual
%GZU %SGZU %Dross/steel %Ash/steel
ash box)
%Plant utilization Lb steel/man-hr
81.8% 498
Kettle capacity Kettle firing Kettle depth/width %lCoating thickness %Spent acid “See text why the actual kettle capacity is so low.
10,000 lb/hr 84.7% 1.29 136’% 38.5%
Kettle
(ratio) is defined as:
Depth/Width
Kettle
Depth/Width
= (kettle
Kettle
= (9ft)/(7ft)
Kettle
Depth/Width
Firing
depth)/(kettle
width)
= 1.29
Ideally the best results overall are for kettle depth/width ratios to be 1.3 to 2.5, especially if lower kettle temperatures are desired. Higher depth/ width ratios and lower kettle temperature normally provide longer kettle lives. ‘Xoating Thickness is defined by: ‘Xoating
Thickness
1 (mils zinc on steel) X (lOOR’Y(3.37 mils)
%,Coating
Thickness
= (4.58 Mils)
%Coating
Thickness
= 136%
X
(100%)/(3.37
mils)
Ideally, this should be as close to 100%) as possible. The above figure of 136% is excellent. The 4.58 mils came from the zinc balance calculation and the 3.37 mils is the standard 2-ozlft” zinc coating. The following formula has been used by the author for 26 years to successfully predict how much “spent” acid is produced under various plant conditions: (The 0.0075 is simply a constant that works.) (Gallons
“Spent”
Acid) = (lb steel) x (0.0075)/ x (steel thickness
(‘2 iron at dump) (Gallons (Gallons
“Spent” Acid) =: (27,409,100 lb) X (0.0075)/(12%)
X
in in.)
(0.22 in.)
“Spent” Acid) = 77,867 gal (predicted)
%Spent Acid is defined by: %Spent Acid = (gal spent actual acid) X (lOO%Y(gal
spent acid predicted)
%Spent Acid = (30,000 gal) X (lOOY~~)/(77,867 gal) #pent
Acid = 38.5%
This is an exceptionally low production of spent acid. The galvanizer attributes this very small vol24
Good Practice 3-6% 45% 0.60% maximum 0.80% (no ash box) 0.40%’ (manual ash box) 0.20% (auto ash box) More than 100% More than 500 (job shop) Up to 1,000 (captive) 25,600 lb/hr (calculated) 100% maximum 1.3-2.5 150% maximum 100%~ maximum
Value
Item
(actual”)
ume to having only one HCl pickling tank. Thus, the steel is never left in the tank for extended periods of time. A single HCl acid pickle tank is very unusual and has considerable risk regarding production capabilities. Likely this low spent acid production is a combination of correct inhibitor usage, high spent acid cost ($2/gall, careful testing, and excellent worker training. Table II shows a summary of the process norms. The “value” is for the galvanizer’s data from Figure 2 and “Good practice” usually results in high-quality product at low cost. GALVANIZING USAGE
TECHNOLOGIES
AND
%GROSS
ZINC
Bad and good aspects of ten new galvanizing technologies are shown in Table III. The %GZU (19841999) are shown in Figure 3. The year that each technology was installed and the quantitative results of each technology are shown in Table IV. As Table IV shows quad flux and a manual ash box reduced zinc usage in 1986-1987 by $804,000/ year. A lower kettle temperature in 1988 reduced zinc usage by $56,00O/year. A high depth/width kettle ratio (1.5 or more) is usually required at a lower kettle temperature to enable high production. Initially, in 1993 Improved Quality Method (IQM) reduced zinc usage $15,00O/year. Interestingly zinc usage dropped in 1994, 1995, 1996, and 1997. The cumulative drop in zinc usage over these four years is $51,000 (now yearly basis). Possible reasons for this steady zinc usage decline are: (a) continuing improvements due to IQM, (b) thicker steel products, and/or (c) better trained, stable labor. Two pieces of information indicate that the 19941997 steady zinc reduction is due to continuing IQM improvements. The first information is subjective, but consistent. After about 100 galvanizers began Metal
Finishing
Table
III. New
Hot-Dip
Galvanizing
Technologies
Technology From “wet” to “dry” kettle
Bad Aspects Requires good flux solutions People think dangerous zinc spatter
Good Aspects Lower %GZU Much less kettle smoke Faster production Much less residual flux on steel
Quad flux (Be 11-14, ACN=1.6, pH=4.2, wetting agent)
Requires good acid rinsing or flux solution purification Requires flux solution testing Requires periodic flux maintenance
Much lower %GZU Thinner zinc on steel Requires flux solution testing Much less zinc spatter Better zinc drainage Less zinc clean-up labor Less dry ash
Lower kettle 845-825°F
Requires (usually
high depth/width 1.5 or greater)
Lower %GZU Thinner zinc coatings on silicon/phosphorus steels
IQM (Improved Quality Method: relates to zinc melt only)
Contract
for use
Slower withdraw 2-3 Wmin
May slow production Requires crane modification
Less zinc clean-up labor Better looking product
May increase
%,GZU
Higher
Contract for use Alloying devices must be maintained More corrosion in salt water NIOSH CDC health hazard OSHA air maximum 0.05 mg/m” Kidney, eyes, GI tract, blood, CNS
Lower Better Lower
Continuing cost (medium) Pimples on steel if lead near 0.5% NIOSH CDC health hazard OSHA air maximum 1 mg/m” Lung and nasal cancer
Lower %GZU Thinner zinc coatings on silicon/phosphorus steels Phosphorus steels More silvery coatings
Continuing costs (moderate) Patented in USA; contract for use
Lower %GZU Better zinc drainage Lower clean-up labor Spangle reappears for lead free Not listed by CDC
Contract
Excellent
Universal
from zinc
racking
Lead alloying
Nickel
temperature
to 1.3% Pb
alloying Ni
0.055%
Bismuth 0.1% Bi
alloying
Spin express CDC
= Center
for Disease
for use
better. In other words, IQM is good after two months but better after two years and even better after five years. The second information that IQM is the cause of the uniform zinc usage decline for 1994 to 1997 is shown in Table V. Note that the year (1993) IQM was started dross and ash increased (0.71% and 0.51%, respectively). These initial dross and ash 2000
Better zinc drainage Higher quality product Less zinc clean-up labor Cleaner threads on bolts Very low operating cost Zero environmental problems
lb/man-hr
production
%GZU zinc drainage clean-up labor
results
in plant
trials
Control
using IQM, the author was curious to know when IQM became most effective. Consistently, galvanizers reported that IQM just keeps getting better and
August
kettle
increases are due to “sins of the past” and are not attributable to IQM. Note that both dross and ash decrease between 1994 to 1997 and for 1997 hit all time lows of 0.39% and 0.38% respectively. The long-term IQM improvements and remarkably low dross and ash production are consistent with the increased fluidity and decreased zinc oxidation afforded by IQM. Table IV shows bismuth 0.1% was started in 1997 and the zinc usage decreased $41,00O/year (net ben25
Table
Year 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
10 z
9
(3 9
f3
a
7 6 5 4 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 YEAR
Figure
3. Percent
gross
zinc
usage
on an annual
basis.
efit; bismuth cost was subtracted from gross to give the $41,000). Since this galvanizer is lead-free he was also pleased that the “spangle” returned. Table Table
IV. Effects
of Technology
Year 1984
%GZU 10.29
1985
11.61
1986
8.38
V. Effects
of Technology/Conditions
%Dross/ Production 1.21 0.48 0.60 0.51 0.49 0.55 0.64 0.71 0.59 0.58 0.44 0.39 0.55 0.64
%A& Production 1.85 0.95 0.64 0.47 0.51 0.57 0.46 0.51 0.47 0.41 0.42 0.38 0.48 0.33
on Dross
and
Ash
Technology Conditions Quad flux and ash box _ Lower kettle temperature Kettle
change
IQM
Bismuth 0.1% Nickel 0.025% and kettle change
V shows an increase in dross and ash production for 1998. It is surprising that the increased zinc fluidity
on %GZU
%GZU Change”
Started
Net $/Year for %GZU Change’
Reasons for %GZU Change No technology/bad plant manager Flux made from “spent” HCl
+1.32
+$204,000
-3.23 June
1986
- $804,000
Quad flux and ash box
- 1.96 1987
6.42
1988
6.75
1989
6.43
1990
6.34
1991
6.55
1992
6.55
1993
6.41
1994
6.35
1995
6.18
Flux getting
bad? Fin coils?
+$51,000
1988?
Lower
temperature
-$56,000
1990
New kettle
+0.33 -0.36
kettle
-0.09 +0.21
likely
under-filled
0 -0.14 -0.06
October
1993
IQM
-$15,000
-0.17 Continuing IQM improvements? Thicker steel products? Better trained, stable labor
-0.06 1996
6.12
1997
6.06
1998
5.70
1999
5.08
2000”
5.20
-$51,000
-0.06 -0.36
August
1997
Bismuth
0.1%
-$41,000
-0.62
October
1998
Nickel 0.025% New kettle over-filled Back to normal %GZU
(-$19,000) +$19,000
+0.12 “%GZU changes are actual from table numbers. ‘Net $/year based on 27,409,100 lb steel/year, $0.565/lb of zinc, change for 12 months before versus 12 months after installation ‘Data for first three months of 2000.
26
includes materials of technology.
costs but not labor
- $75,000
costs,
and based
on average
Metal
%sGZU
Finishing
Table
VI. Galvanizing
cost Capital and interest Energy Administrative Maintenance Zinc Labor Supplies Spent acid Total
Costs Tse
Fixed for nine years Mostly fixed Fixed Mostly fixed Variable Variable Variable Variable
(due to bismuth) would cause more dross. Because nickel was started so quickly after bismuth, it is not known if the dross increase would have gone back down to normal. Ash production of 0.33% for 1999 is excellent. As shown in Table IV additions were started in 1998. Initially 0.055% nickel was used but the galvanizer experienced some zinc peeling problems on thick steel products (from several different clients), which the galvanizer blamed on nickel. Later he reduced the nickel to 0.025% and is happy with the $75,00O/year lower zinc cost (net nickel cost was subtracted from gross savings to give the $75,000). Table V shows an additional dross increase (from 0.55% for 1998 to 0.64% for 1999), which is consistent with literature reports of increased dross using nickel. The reader should note that lung and nasal cancer can result from nickel. The author found 0.078% nickel in this galvanizer’s ash and 0.45% nickel in his dross. The ash could produce an airborne hazard, whereas the dross is not likely to become airborne. Interestingly, the OSHA maximum allowable for nickel is 1 mg/M3 (causes cancer), whereas the maximum allowable for lead is only 0.05% mg/M3 (causes kidney, eye, gastrointestinal, blood, and central nervous system difficulties). Another galvanizer (prime western) using a manual ash box had 0.052% airborne lead (so the ash box was taken away). The lower zinc usage caused by the new technologies apply only to this galvanizer. Steel types and steel geometries vary greatly and the choice of which technology to adopt first greatly affects the attainable benefits. For example, IQM or nickel zinc can cause a dramatic lowering of zinc usage for a galvanizer with especially bad flux solution. In a future article the author will examine a galvanizer with very bad flux solution but attains low %GZU using most of these technologies. His rejects are, however, unacceptably high. August
2000
Cents/Lb 2.59 cents 0.76 cents 0.37 cents 0.36 cents 2.88 cents 2.91 cents 0.55 cents 0.22 cents 10.64 cents
$/Year
$711,000 $209,000 gE%i: $7881500
;22::: $60,600
$2,918,500
GALVANIZING
% cost 24.3%
7.1% 3.5% 3.4%
27.1% 27.3% 5.2%
2.1% 100.0%
COSTS
Costs for the galvanizer (Fig. 2 data) are shown in Table VI. For a “bare-bones” plant using hydrochloric acid pickling in a warm climate (no acid flume exhaust and no central heating) the general rule of thumb for building a plant is $lOO,OOO/ft of kettle length. Thus, this plant cost about $lOO,OOO/ft X 32 ft equals $3.2 million. At 8% interest for 9 years (1.08 raised to the power 9) the interest equals the principle. Then $6.4 million must be paid back to the lender divided by 9 equal payments of $711,000 ($6.4 million). The $711,000/27,409,100 lb equals $O.O259/lb equals 2.59 cents/lb of steel (for capital and interest). Readers may question energy cost as being “mostly fixed.” Very detailed calculations, which have given accurate results for many years, show that if production doubled from 27 million lb of steel to 54 million lb of steel then the total energy cost will increase only 20% (from $209,00O/year-$251,000/ year). Future articles will deal with these calculations. The remainder of the cost items in Table VI comes directly from Figure 2 or from phone conversations with the galvanizer. Considering the actual total cost of 10.64 cents/lb steel galvanized, it is difficult to understand how some galvanizers can profit by charging 8 to 10 cents/lb of steel. RECOMENDATIONS
FOR
THE
GALVANIZER
From Figure 2 the galvanizer is not using the technologies, universal racking, or slow steel withdrawal from the molten zinc. These two technologies are likely to increase lb/man-hour by faster production and less zinc clean-up. These two technologies likely would reduce costs more than $lOO,OOO/year. Slow withdrawal from the zinc is especially important for long steel products like pipe. For example, a 6-in. diameter 40-ft-long pipe withdrawn 20” from horizontal at 5 ft/min will have the zinc flow along the outside and out the inside at 14.6 ft/min. The resulting outside and inside drain lines are usually an average of 0.5 in. wide by 0.125 in. thick 27
Table
VII. Energy
Savings
Item Caustic tank Flux tank
Modification Insulate sides and ends Heat recovery from kettle flue to heat flux
Kettle heat
Convert from flat flame (50% eff.) to end firing (67% eff..) insulation under kettle and around furnace
Electricity Total
Current Energy $/Year
Future Energy $Near
$22,600 $38,600
$17,500
Savings $Near $5,100 $38,600
gas ($10,000 electricity for compressor) $113,000
($2,000 est. electricity to pump water) $84,400
$28,600
$35,000
$27,000
$209,200
$128,900
$8,000 $80,300
(heavier drain line at last take out). If this pipe has a 3-mil zinc coating, then there will be 14.0 lb of zinc in the coating and 15.5 lb of zinc in the two drain lines. The two drain lines are greatly reduced (go flat) with slow withdrawal. From experience long steel products and spin products benefit most from technologies that improve zinc drainage (e.g. quad flux, IQM, lead, and bismuth). Table VII shows energy savings by insulating the sides and ends of the caustic tank, heating the flux using waste kettle flue heat, converting the kettle furnace from flat flame (50% efficiency) to end fired (67% efficiency), insulating under the kettle (6-in. rigid high-strength insulation), and insulating the outside of the kettle furnace. The predicted $80,30O/yr savings would reduce galvanizing cost by 0.29 cent/lb steel. At present the galvanizer uses only “word-ofmouth” advertising. His product is excellent. It is not okay to have excellent product in your backyard if nobody knows about it. This is just plain bad
business. Hot-dip galvanizing is a business and like any business, advertising is required. A reasonable profit from a single job can pay many times over the advertising costs to get the job. THANKS
TO THE
GALVANIZER
The author sincerely thanks the owner/operator of the galvanizing plant. His cooperation and patience are greatly appreciated. The author is pleased to have been a part of the very great success that this owner has achieved. This owner/operator and his plant are without question one of the best three in North America. They are good friends. BIOGKAPHV
Thomas H. Cook has a Ph.D. in inorganic chemistry from the University of Wyoming and has taught chemistry at the university level for 20 years. He has presented Hot-Dip Galvanizing Workshops and consulted world-wide for 26 years. MZJ
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information
l5ton 20ton 30ton 40ton 50ton 60ton 80ton 100ton 130ton 150ton 170ton
$8994 12,029 14,667 20,108 25.182 281873 35,532 42,940 52,727 58,264 61,179
210ton 255ton 290ton 360ton 420ton
72,906 89,326 101,751 125,507 136,295
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